Wireless communications systems are delivering ever increasing content to consumers. In the field of wireless communications devices may be classified as licensed or unlicensed. This typically relates to the spectrum in which the device operates. Recently, there have been new types of communications technology that do not fit into the traditional regime. Some of these devices are capable of reusing frequencies that are typically licensed spectrum.
One example of these devices is a technology commonly referred to as Ultra-Wideband. This technology takes many forms but is characterized by very low power emissions across significantly large frequency bands. In the United States, the Federal Communications Commission (FCC) has allowed these types of devices to intentionally transmit in frequencies typically licensed to other services. The transmission is significantly limited in power and therefore the devices do not pose significant interference risks to other incumbent users of the spectrum.
Recently, the FCC has allowed the reuse of frequencies normally assigned to television broadcasters. This reuse by unlicensed transmitters, is limited to specific geographical regions where television broadcasters are not present. Once again the transmissions are power and frequency band limited and pose no significant interference risk to incumbent users. In the U.S. the broadcast television spectrum is broken up into 6 MHz channels beginning around 50 MHz and extending up to 700-800 MHz. The spectrum is not continuous and other users, such as FM Radio, are within this spectrum with broadcast television.
In the design of wireless communications systems, design choices must be made as to the type of modulation used. Modulation, as is known in the art, is the process of encoding information on a signal that is to be transmitted. Typically, the transmitter modulates data onto the signal and transmits. A receiver then demodulates the data from the received signal. The choice of modulation impacts a number of communication parameters. For example, a selection of Binary Phase Shift Keying as a modulation technique can limit the transmission to one of two phases and therefore a single bit of information per signal. Other techniques may encode more information per signal and often modulation techniques can be classified by their ability to carry information in a constrained bandwidth. This “bandwidth efficiency” is often expressed in bits-per-Hertz. Another parameter that is impacted by the selection of a modulation technique is the spectrum the signal occupies. In many situations, present communication technologies, when operating in the television frequency bands, will be inefficient in their ability to carry large amounts of data.
Therefore there exists a need for a system, and methods for improved wireless communications.